Amorphous bonding distance

Solid state NMR is a relatively recent spectroscopic technique that can be used to uniquely identify and quantitate crystalline phases in bulk materials and at surfaces and interfaces. While NMR resembles X-ray diffraction in this capacity, it has the additional advantage of being element-selective and inherently quantitative. Since the signal observed is a direct reflection of the local environment of the element under smdy, NMR can also provide structural insights on a molecularlevel. Thus, information about coordination numbers, local symmetry, and internuclear bond distances is readily available. This feature is particularly usefrd in the structural analysis of highly disordered, amorphous, and compositionally complex systems, where diffraction techniques and other spectroscopies (IR, Raman, EXAFS) often fail. 

Given the above definition of a bond distance, we can analyze species lifetimes. The lifetime of all species is less than 12 fs above 2.6g/cc, which is roughly the period of an O-H bond vibration (ca. 10 fs). Hence, water does not contain any molecular states above 75 GPa and at 2000 K but instead forms a collection of short-lived transient states. The L simulations at 2.6g/cc (77 GPa) and 2000 K yield lifetimes nearly identical to that found in the S simulations (within 0.5 fs), which indicates that the amorphous states formed from the L simulations are closely related to the superionic bcc crystal states found in the S simulations. 

Traditionally, X-ray absorption edge measurements have been used to determine oxidation states of metals in complex materials. The extended X-ray absorption fine structure (EXAFS), on the other hand, provides structural information such as bond distances and coordination numbers even with powdered samples, crystalline or amorphous, the fine structure essentially resulting from short-range order around the absorbing atom. The technique is also useful for studying solid surfaces (SEXAFS). The observation of fine structure beyond the K-absorption edges of materials dates back to... 

Another approach to help facilitate crystallisation is to bias the tr ectories of all the atoms moving in the (molten/amorphous) configuration to favour crystallisation. Specifically, order parameters (which can be bond distances, coordination numbers, nearest neighbour densities and radial distribution functions) may be used as a gauge of crystallinity and used to help drive the simulation (trajectory) to favour maximising the order parameter and, ultimately, induce crystallinity. 

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